Thermal design considerations for electronic equipment, such as a large scale computer system, involve primary concerns for performance, cost, reliability and low maintenance. In practice, performance requirements, on the one hand, are weighed against the remaining concerns, on the other. A system characterized by simplicity, but having the ability to provide adquate cooling of the electronic equipment, represents the best solution to the thermal problem. Air cooling is generally regarded as the most simple and reliable system. However, as the power density on the computer cards continually increases, it becomes increasingly more difficult to cool with air.
In the typical forced air cooling scheme, air is blown across the computer card in a direction parallel to the planar surface of the card. As the air travels across the card, it picks up heat in serial fashion, from the integrated circuit packages mounted thereon and the air increases in temperature. With the rise in card power levels, large volumes of air are needed to keep the air temperature rise from exceeding acceptable levels.
The cooling problem is further exacerbated by the increase in power and size of the integrated circuit packages. The high power levels of the last mentioned devices result in higher than average local temperature rises. Each pocket of high temperature air is directed by the air stream onto the next package. Also, as the devices become physically larger, they tend to block the flow of cooling air from the downstream packages. Because of the last mentioned thermal effects, every package forms a downstream wake of high temperature, low velocity air. With the high density packaging of present day electronic equipment, it is apparent that the downstream packages will fall directly within this wake. Moreover, these thermal effects become more difficult to control in proportion to the increase in physical size and power dissipation of the integrated circuit packages. Ultimately, in new computer design applications, the package and card power levels may overwhelm the cooling reasonably expected to be provided by the above-described, serially directed air stream. In such a case, more exotic cooling systems, such as those employing a water approach may be considered, notwithstanding the increase in complexity and cost and decrease in reliability of such systems.
What is desired is a cooling system which utilizes air as the cooling medium, but which differs from the conventional approach in its ability to maintain acceptable temperature levels in present day high density electronic equipment. The parallel-flow air system of the present invention fills such a need.